This invention relates to a master cylinder used to supply fluid pressure to a hydraulic system and, more particularly, it relates to a master cylinder adapted for use in an automative hydraulic brake system which provides a gradual transition from a low pressure, high volume stage of operation for taking up the slack in the brake system to a high pressure low volume movement for applying the brakes.
Dual ratio master cylinders have been known in the brake art for some time. The main purpose for such a device is to bridge the gap presently existing in the market between brake systems of the power assist type and manual braking systems with no assist. The aim of such systems is to provide a brake master cylinder that will require less pedal effort with the same foot travel as existing manual master cylinders and to require lower pedal effort to power assisted systems when the power assist is inoperative.
Certain inherent faults in prior art dual ratio master cylinders have prevented their widespread adoption by the automotive industry in spite of the need such a device would fill. These shortcomings include a sharp transition from one stage to another which can be detected at the brake pedal by the operator's foot, premature transition from one stage to another when brakes are improperly adjusted, the lack of a fail-safe switchback feature whereby the device could return from second stage application to first stage application if either the brake system or master cylinder developed a leak under pressure and premature actuation of the second stage due to a sudden application of the brake pedal.
Some approaches to solving individual phases of these problems have been successful but no device has been produced which has been acceptable to the Automotive Industry which overcomes all of the objections raised while accomplishing all of the advantages sought.